Multiple Functioning Proteins
Country: United States
Date: January 2009
How is it possible to have two proteins that have two
different functions that are made of exactly the same amino acids?
Proteins often consist of multiple parts, known as domains, that have
distinct functions, so a single protein may have multiple functions in
the cell. For example, proteins called transcription factors regulate
the expression of genes by having a domain which binds the DNA as well
as a different domain which binds the machinery of the cell that is
involved in transcribing the gene.
There are plenty of examples of proteins which function in disparate
pathways. One of the most intensely studied genes in the human
genome, p53, is one of the most important genes in cancer biology and
is thought to consist of seven domains. p53 acts as a transcription
factor and, upon cell damage, binds DNA to induce the expression of
genes which prevent the cell from dividing. In addition, cell damage
can lead p53 to interact with and activate proteins involved in
programmed cell death, also known as apoptosis. By having domains
which are involved in these two distinct functions, stopping damaged
cells from dividing and causing them to "commit suicide," p53 plays a
key role in preventing damaged cells from becoming tumors.
First of all, if two "different " enzymes have the same amino acid sequence,
they are not different. Although I don't know of any examples of an enzyme or
protein with two different functions, if one exists, it could be explained by
the fact that the genes for two different proteins became fused during evolution
and now these "two" proteins are fused and retain the two functions of the
formerly separate proteins.
Ron Baker, Ph.D.
There are many nutrients, including proteins, that perform multiple functions.
If there had to be one and only one specific protein for every life function, I
don't think we would be here -- at least not in our present form.
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Update: June 2012